Holographic digital data storage system compatible with holographic and reflective medium

ABSTRACT

In a holographic digital data storage system, a light source generates a reference beam, a holographic optical element saves a plurality of interference patterns between the reference beam and a plurality of beams of specific sizes and a beam splitter splits each reproduced beam into a holographic signal beam and a holographic reference beam. A medium records an interference pattern between the holographic reference beam and the holographic signal beam and reflecting the holographic reference beam to generate a reflective information beam and, if only the holographic reference beam is illuminated, a displaying means displays a holographic reproduced beam for the holographic signal beam and detecting the reflective information beam.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. Ser. No.09/815,046 filed on Mar. 23, 2001, now U.S. Pat. No. 6,999,397, whichclaims priorities thereon pursuant to 35 USC 120.

FIELD OF THE INVENTION

The present invention relates to a holographic digital data storagesystem; and, more particularly, to a holographic digital data storagesystem compatible with a CD/DVD player.

BACKGROUND OF THE INVENTION

Recently, there have been reported increasing levels of activeresearches on holographic digital data storage systems triggered by thedevelopment of semiconductor lasers, charge coupled devices (CCDs),liquid crystal displays (LCDs) and the like. Since the holographicdigital data storage system normally features a large storage capacityand high data transfer rate, it has already been applied to, e.g.,fingerprint recognition systems for storing and reproducingfingerprints, and the scope of its applications keeps expanding.

The holographic digital data storage system allows a signal beamtransmitted from an object to interfere with a reference beam, andwrites interference patterns generated from such interference phenomenaon a storage medium such as a crystal or a photopolymer which reactsdifferently depending on the amplitude and phase of an interferencepattern. In the holographic digital data storage system, the phase ofthe signal beam as well as the amplitude thereof may be recorded bychanging an incident angle of the reference beam, so that a threedimensional display of an object can be realized. Further, hundreds tothousands of holographic digital data comprised of binary data on apage-by-page basis can be stored in a single space of the storagemedium.

FIG. 11 depicts an overall block diagram of a holographic digital datastorage system, wherein the holographic digital data storage systemcomprises a light source 20, a beam expander 21, a beam splitter 22, tworeflection mirrors 23 and 24, a spatial light modulator (SLM) 25, amedium 26 and a CCD 27.

The light source 20 generates an optical signal, e.g., a laser beam,whose wavelength falls within a specific wavelength band required forthe holographic digital data. The beam expander 21 expands the size ofthe laser beam.

The beam splitter 22 separates the expanded laser beam into a referencebeam and a signal beam and transfers the reference beam and the signalbeam through two different transmission channels, wherein the referencebeam and the signal beam correspond to a transmitted beam and areflected beam, respectively.

The reference beam is reflected at the reflection mirror 24 so that thereflected reference beam is transferred to the medium 26. The signalbeam, on the other hand, is reflected at the reflection mirror 23 sothat the reflected signal beam is transferred to the SLM 25. The SLM 25modulates the reflected signal beam into binary pixel data on a pagebasis. The modulated signal beam is transferred to the medium 26. Incase the reflected signal beam is, for example, image data provided on aframe basis, the reflected signal beam is preferably modulated on aframe basis and the reflection mirror 24 functions to change thereflection angle of the reflected reference beam by a small amount.

The medium 26 stores the interference pattern acquired from aninterference phenomenon between the reflected reference beam and themodulated signal beam, wherein the interference pattern depends on thereflected signal beam, i.e., the data inputted to the SLM 25. In otherwords, the modulated signal beam irradiated to the medium 26 ismodulated on a page basis and the reflected reference beam is reflectedin an angle corresponding to the modulated signal beam. The modulatedsignal beam interferes with the reflected reference beam within themedium 26. The amplitude and phase of the interference pattern resultsin a photo-induction within the medium 26 so that the interferencepattern may be written on the medium 26.

When only the reference beam is irradiated onto the medium 26 in orderto reconstruct the data written thereon, the reference beam isdiffracted by the interference pattern within the medium 26 so that acheck pattern with original brightness on a pixel basis may be restored.When the check pattern is irradiated on the CCD 27 in turn, the originaldata may be restored. The reference beam used for reproducing the datawritten on the medium 26 should be irradiated at the same incident angleas that of the reference beam when recording the data on the medium 26.

FIG. 12 presents a block diagram of a conventional CD or DVD player,wherein the CD/DVD player comprises a high frequency overlap module 10,two mirrors 11 and 18, a polarizing prism 12, a cylindrical lens 13, aphotodiode (PD) 14, a λ/4 plate 15, a disc medium 16, an object lens 17and a collimating lens 19. A detailed description for the structure andthe operational principle of such CD/DVD player will be omitted heresince it is well known to a person having ordinary skill in the relevantart.

As for the conventional CD/DVD player of FIG. 12 and the conventionalholographic digital data storage system of FIG. 11, however, there hasbeen found a drawback in that they cannot be compatible with each othersince the positions of their detectors, e.g. optical diodes, aredifferent from each other. To be specific, since the CD/DVD player hasits detector along a direction of reflection while the holographicdigital data storage system has its detector along a transmissiondirection, a single detector cannot be used for both systems. Further,the size difference of beams used in the two systems is so great thattwo different optical instruments are required.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide aholographic digital data storage system compatible with a CD/DVD playerby using a holographic optical element with a plurality of beam sizesand numerical apertures produced by employing a spatial multiplexingtechnique or an angular multiplexing technique.

In accordance with a preferred embodiment of the present invention,there is provided a holographic digital data storage system comprising:

a light source for generating a reference beam;

means for saving a plurality of interference patterns between thereference beam and a plurality of beams of specific sizes and, if onlythe reference beam is illuminated, generating a plurality of reproducedbeams corresponding to the plurality of beams of specific sizes;

means for splitting each reproduced beam into a reflected beam and atransmitted beam and assigning one of the reflected beam and thetransmitted beam as a holographic reference beam;

means for modulating the other of the reflected beam and the transmittedbeam into a holographic signal beam corresponding to a holographic inputsignal;

means for recording an interference pattern between the holographicreference beam and the holographic signal beam and reflecting theholographic reference beam to generate a reflective information beam,wherein the reflective information beam proceeds along an oppositedirection to the holographic reference beam; and

means for, if only the holographic reference beam is illuminated,displaying a holographic reproduced beam for the holographic signal beamand detecting the reflective information beam.

In accordance with another preferred embodiment of the presentinvention, there is provided a holographic digital data storage systemcomprising:

a light source for generating a reference beam;

means for adjusting a polarization of the reference beam to generate amultiplicity of polarized beams with a multiplicity of polarizationcomponents, respectively;

means for storing a number of interference patterns between themultiplicity of polarized beams and a number of reflective beams ofspecific sizes and between the multiplicity of polarized beams andholographic beams of specific sizes, wherein the holographic beams ofspecific sizes have the multiplicity of polarization components, and, ifthe multiplicity of polarized beams are illuminated, generatingreflective reproduced beams corresponding to the reflective beams ofspecific sizes and holographic reproduced beams corresponding to theholographic beams of specific sizes, wherein the holographic reproducedbeams have a multiplicity of holographic polarization componentstransferred through separate paths;

means for collimating the polarization directions of the holographicreproduced beams to generate a first and a second holographic beam,wherein one of the first and the second beam is used as a holographicreference beam;

means for modulating the other of the first and the second beam into aholographic signal beam corresponding to holographic input signals;

means for recording an interference pattern between the holographicreference beam and the holographic signal beam and reflecting thereflective reproduced beams to generate reflective information beams,wherein the reflective information beams proceed along an oppositedirection of the reflective reproduced beams;

means for, if only the holographic reference beam is illuminated,displaying a holographic reproduced beam for the holographic signal beamand detecting the reflective information beams; and

means for introducing the reflective reproduced beam into said recordingmeans and transferring the reflective information beams into saiddisplaying.

In accordance with still another preferred embodiment of the presentinvention, there is provided a holographic digital data storage systemcomprising:

a light source for generating a reference beam;

means for splitting the reference beam into a first and a second beam toproceed through separate paths;

means for modulating the first beam into a holographic signal beamcorresponding to holographic input signals;

means for storing a number of interference patterns between the secondbeam and reflective beams of specific sizes and between the second beamand a holographic beam of specific size and, if the second beam isilluminated, generating reflective reproduced beams corresponding to thereflective beams of specific sizes and a holographic reproduced beamcorresponding to the holographic beam of specific size, wherein theholographic reproduced beam functions as a holographic reference beam;

means for recording an interference pattern between the holographicreference beam and the holographic signal beam and reflecting thereflective reproduced beams to generate reflective information beams,wherein the reflective information beams proceed along an oppositedirection of the reflective reproduced beams;

means for, if only the holographic reference beam is illuminated,displaying a holographic reproduced beam for the holographic signal beamand detecting the reflective information beam; and

means for introducing the reflective reproduced beams into saidrecording means and turning the reflective information beams into saiddisplaying means.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of preferred embodimentsgiven in conjunction with the accompanying drawings, in which:

FIG. 1 presents a block diagram of a holographic digital data storagesystem compatible with a CD/DVD player in accordance with a firstembodiment of the present invention;

FIG. 2 describes an embodiment of the holographic beam splitter shown inFIG. 1;

FIG. 3 illustrates a block diagram of a holographic digital data storagesystem compatible with a CD/DVD player in accordance with a secondembodiment of the present invention;

FIG. 4 demonstrates an embodiment of the holographic polarized beamsplitter shown in FIG. 3;

FIG. 5 represents a block diagram of a holographic digital data storagesystem compatible with a CD/DVD player in accordance with a thirdembodiment of the present invention;

FIG. 6 explains an embodiment of the holographic polarized beam splittershown in FIG. 5;

FIG. 7 shows a block diagram of a holographic digital data storagesystem compatible with a CD/DVD player in accordance with a fourthembodiment of the present invention;

FIG. 8 sets forth an embodiment of the holographic polarized beamsplitter shown in FIG. 7;

FIG. 9 provides a block diagram of a holographic digital data storagesystem compatible with the CD/DVD player in accordance with a fifthembodiment of the present invention;

FIG. 10 exhibits an embodiment of the holographic optical element shownin FIG. 9;

FIG. 11 displays a block diagram of a conventional holographic digitaldata storage system; and

FIG. 12 depicts a block diagram of a conventional CD/DVD player.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram of a holographic digital data storage system100 in accordance with a first embodiment of the present invention whichis compatible with a CD/DVD player, wherein the holographic storagesystem 100 comprises a light source 102, a holographic beam splitter104, a beam splitter 106, three lenses 108, 124, 126, a medium 110, twomirrors 112, 120, a charge coupled device (CCD) 114, a photodiode (PD)116, a shutter 118 and a spatial light modulator (SLM) 122.

The light source 102 is an essential element for the writing andreconstruction process of the holographic digital data storage system. Alaser, for example, can be used as the light source. The light source102 provides an optimum wavelength band for the medium 110 of theholographic digital data storage system. An available wavelength banddepends on a photo-sensitizer and an initiator added to the medium 110.

The holographic beam splitter 104 is made of a same material as used ina holographic memory. The beam from the light source 102 is used as areference beam. If a beam of a specific size is introduced to theholographic beam splitter 104 with a predetermined angle with respect tothe reference beam, an interference pattern between the reference beamand the beam of the specific size is recorded within the holographicbeam splitter 104.

Referring to FIG. 2, there is illustrated an embodiment of theholographic beam splitter 104 which may be made by employing an angularmultiplexing technique. It is assumed that three reference beams B_(REF)^(CD), B_(REF) ^(DVD), B_(REF) ^(HDDS) are introduced, wherein the threereference beams B_(REF) ^(CD), B_(REF) ^(DVD), B_(REF) ^(HDDS) havedifferent incident angles but have a same wavelength. If the threereference beams B_(REF) ^(CD), B_(REF) ^(DVD), B_(REF) ^(HDDS) and theircorresponding beams of specific sizes B_(CD), B_(DVD), B_(HDDS) areintroduced with predetermined relative angles, respectively, theinterference patterns between three reference beams B_(REF) ^(CD),B_(REF) ^(DVD), B_(REF) ^(HDDS) and their corresponding beams ofspecific sizes B_(CD), B_(DVD), B_(HDDS) are recorded within theholographic memory by using the angular multiplexing method. The beamsizes and shapes of beams of specific sizes B_(CD), B_(DVD), B_(HDDS)depend on the medium on which they are recorded. If only the threereference beams B_(REF) ^(CD), B_(REF) ^(DVD), B_(REF) ^(HDDS) areintroduced at corresponding predetermined respective angles to theholographic memory in which the interference patterns have beenrecorded, three reproduced beams B_(CD) ^(RE), B_(DVD) ^(RE), B_(HDDS)^(RE) for three beams of specific sizes B_(CD), B_(DVD), B_(HDDS) aregenerated. The intensities of the three reproduced beams B_(CD) ^(RE),B_(DVD) ^(RE), B_(HDDS) ^(RE) may be represented as diffractionefficiencies of the interference patterns. The diffraction efficiency inphotopolymer may be substantially 100%.

A beam factor BF of the CD/DVD player should be constant for theholographic digital data storage system and the CD/DVD player to becompatible. In general, the beam factor B_(F) of the CD player is0.57690 □m⁻¹ and the beam factor B_(F) of the DVD player is 0.9230 □m⁻¹.The beam factor B_(F) can be calculated as follows:

$\begin{matrix}{B_{F} = \frac{N.A.}{\lambda}} & {{Eq}.\mspace{14mu} 1}\end{matrix}$wherein λ and N.A. represent a wavelength of the beam and a numericalaperture, respectively. When a different wavelength is used, the N.A.can be adjusted in such a way that the B_(F) remains constant and thusthe CD/DVD player can be played. The N.A. is calculated as follows:N.A.=n·sin α  Eq. 2wherein n represents a refractive index of a material filled behind thelens through which the beam passes and αrepresents a concentration anglewith respect to an optical axis, i.e., a central axis, of the lens incase an incident beam vertical to the lens is concentrated on a focus.In other words, sin α is a function of the focal length F of the lensand a beam width W of the beam incident into the lens and is given asfollows:

$\begin{matrix}{{\sin\;\alpha} = \frac{W}{2\sqrt{\left( \frac{W}{2} \right)^{2} + F^{2}}}} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

Accordingly, the beam width W can be derived from the followingequation:

$\begin{matrix}{W = {\frac{2{FB}_{F}\lambda}{n} \cdot \frac{1}{\sqrt{1 - \left( \frac{B_{F}\lambda}{n} \right)^{2}}}}} & {{Eq}.\mspace{14mu} 4}\end{matrix}$

Consequently, the B₁, can be sustained at a constant value bycontrolling the beam width W and thereby adjusting the N.A., so that theCD/DVD player can be played.

When a laser beam having a wavelength λ of 532 nm is transmitted throughthe air whose refractive index is 1 and a lens with a focal length F of1 cm is employed, a beam factor B_(FCD) for the CD player and a beamfactor B_(FDFD) for the DVD player are 0.5769 μm⁻¹ and 0.9230 μm⁻¹ ,respectively. Accordingly, the beam widths W_(CD) and W_(DVD) requiredin the CD/DVD player are calculated as follows, respectively:

$\begin{matrix}{W_{CD} = {\frac{2\left( {1\mspace{14mu}{cm}} \right)\left( {0.5769\mspace{14mu}{\mu m}^{- 1}} \right)\left( {0.532\mspace{14mu}{\mu m}} \right)}{\sqrt{1 - {\left( {0.5769\mspace{20mu}{\mu m}^{- 1}} \right)^{2}\left( {0.532\mspace{14mu}{\mu m}} \right)^{2}}}} = {0.64495\mspace{14mu}{cm}}}} & {{Eq}.\mspace{14mu} 5} \\{W_{DVD} = {\frac{2\left( {1\mspace{14mu}{cm}} \right)\left( {0.9230\mspace{14mu}{\mu m}^{- 1}} \right)\left( {0.532\mspace{14mu}{\mu m}} \right)}{\sqrt{1 -}\left( {0.9230\mspace{20mu}{\mu m}^{- 1}} \right)^{2}\left( {0.532\mspace{14mu}{\mu m}} \right)^{2}} = {1.12734\mspace{14mu}{cm}}}} & {{Eq}.\mspace{14mu} 6}\end{matrix}$The beam widths W_(CD)/W_(DVD) for the beams of specific sizes B_(CD),B_(DVD) are 0.64495 cm and 1.12734 cm, respectively.

When an Nd-YAG laser beam having a wavelength λ of 650 nm is transmittedthrough the air whose refractive index is 1 and a lens with a focallength F of 1 cm is employed, the beam widths W_(CD) and W_(DVD)required in the CD/DVD player are calculated as follows, respectively:

$\begin{matrix}{W_{CD} = {\frac{2\left( {1\mspace{14mu}{cm}} \right)\left( {0.5769\mspace{14mu}{\mu m}^{- 1}} \right)\left( {0.650\mspace{14mu}{\mu m}} \right)}{\sqrt{1 - {\left( {0.5769\mspace{20mu}{\mu m}^{- 1}} \right)^{2}\left( {0.650\mspace{14mu}{\mu m}} \right)^{2}}}} = {0.80900\mspace{14mu}{cm}}}} & {{Eq}.\mspace{14mu} 5} \\{W_{DVD} = {\frac{2\left( {1\mspace{14mu}{cm}} \right)\left( {0.9230\mspace{14mu}{\mu m}^{- 1}} \right)\left( {0.650\mspace{14mu}{\mu m}} \right)}{\sqrt{1 -}\left( {0.9230\mspace{20mu}{\mu m}^{- 1}} \right)^{2}\left( {0.650\;{\mu m}} \right)^{2}} = {1.49980\mspace{14mu}{cm}}}} & {{Eq}.\mspace{14mu} 6}\end{matrix}$The beam widths W_(CD)/W_(DVD) for the beams of specific sizes B_(CD),B_(DVD) are 0.80900 cm and 1.49980 cm, respectively.

The beam size can be adjusted for both a holographic mode and a CD/DVDmode with a same wavelength by using the holographic beam splitter 104.

In the holographic mode, the reference beam B_(REF) ^(HDDS) isintroduced to the holographic beam splitter 104 with a predeterminedincident angle. The holographic beam splitter 104 generates a reproducedbeam B_(HDDS) ^(RE) corresponding to the reference beam B_(REF) ^(HDDS)and the beam of specific size B_(HDDS); and the beam splitter 106 splitsthe reproduced beam B_(HDDS) ^(RE) into a reflected beam and atransmitted beam. The reflected beam is illuminated into the medium 110through a path A. The shutter 118 on the path A may operate to transmitthe reflected beam only in the recording state of the holographic modeand not in the reproduction state of the holographic mode. After beingtransmitted through the shutter 118, the reflected beam is reflectedagain by the mirror 120 and modulated by the SLM 122 in order tocorrespond to input signals so that a holographic signal beam isgenerated. The holographic signal beam is focused to the medium 110 bythe lens 124. In the meantime, the transmitted beam is illuminatedthrough the path B to the medium 110 as a holographic reference beam,wherein the lens 108 functions to concentrate the holographic referencebeam. The interference pattern between the holographic reference beamand the holographic signal beam is recorded on the medium 110.

The medium 110 may be movable upwards or downwards so that the beam maybe focused in front of or in the rear of the medium 110 by the lenses124 and 108. For example, in case a shift multiplexing principle isused, the beam is preferably focused in front of the medium 110 by thelenses 124 and 108 in the holographic mode while the beam may bepreferably focused in the rear of the medium 110 in the CD/DVD mode. Incase two lenses with two different focal distances are used, a lens witha shorter focal distance may be preferably used for the holographicmode, if necessary, while the other lens with the longer focal distancemay be used for the CD/DVD mode.

In the reproduction state of the holographic mode, the shutter 118 isshut off so that only the transmitted beam is introduced to the mediumthrough the path B. Since the transmitted beam functions as theholographic reference beam, a holographic reproduced beam is produced inan original direction of the holographic signal beam introduced into themedium 110 in the recording state. The holographic reproduced beam isfocused by the lens 126 and displayed on the charge coupled device (CCD)114.

In the CD/DVD mode, the holographic beam splitter 104 is rotated by apredetermined angle so that the reference beam B_(REF) ^(CD)/B_(REF)^(DVD) may be introduced and, therefore, the reproduced beam B_(CD)^(RE)/B_(DVD) ^(RE) corresponding to the reference beam B_(REF)^(CD)/B_(REF) ^(DVD) is generated by the holographic beam splitter 104.The beam splitter 106 divides the reproduced beam B_(CD) ^(RE)/B_(DVD)^(RE) into a reflected beam and a transmitted beam and the shutter 118makes the reflected beam shut off. The transmitted beam is introducedinto the CD/DVD medium 110 through the lens 108 after passing throughthe path B. The beam factor B_(F) of the beam has previously beencontrolled before the beam is introduced to the medium 110. The beam isreflected by the medium 110 to generate a CD/DVD reproduced beam and theCD/DVD reproduced beam is transferred through the path B. The CD/DVDreproduced beam is reflected and transmitted again by the beam splitter106 to generate a reflected reproduced beam and a transmitted reproducedbeam. The transmitted reproduced beam is transferred to the holographicbeam splitter 104 so that it does not affect the reproduction signal.Accordingly, the reflected reproduced beam proceeds along the path C tobe detected by the photodiode 116 or the CCD 114.

Referring to FIG. 3, there is illustrated a block diagram of aholographic digital data storage system 300 in accordance with a secondembodiment of the present invention which is compatible with a CD/DVDplayer, wherein the holographic storage system 300 comprises a lightsource 302, a λ/2 plate 303, a holographic polarized beam splitter 304,a beam splitter 306, three lenses 308, 324, 326, a medium 310, twomirrors 312, 320, a charge coupled device (CCD) 314, a photodiode (PD)316, a shutter 318, a beam expander 321 and a spatial light modulator(SLM) 322. In comparison with the first embodiment illustrated in FIG.1, the λ/2 plate 303, the holographic polarized beam splitter 304 andthe beam expander 321 are added.

The λ/2 plate 303 allows the polarization direction of the linearlypolarized beam introduced from the light source 302 to be rotated by apredetermined angle. The beam with the rotated polarization direction isintroduced to the holographic polarized beam splitter 304.

The holographic polarized beam splitter 304 is made of a higherbirefringence material such as LiNbO₃ or BaTiO₃. Since the refractiveindex difference between the ordinary beam and the extraordinary beammay be used, the reproduced beams may be selectively generated inaccordance with the reference beams with different polarizationdirections.

Referring to FIG. 4, there is illustrated an embodiment of theholographic beam splitter 304 made by using the birefringencecharacteristics. It is assumed that CD/DVD horizontal/vertical polarizedbeams of specific sizes B_(CD&DVD) are used to reproduce the CD playerand the DVD player. The CD/DVD horizontal/vertical polarized beams ofspecific sizes B_(CD&DVD) have the beam sizes and the beam shapesrequired in the CD player and the DVD player, respectively. Thehorizontal/vertical polarized reference beams B_(REF) are introducedfrom the λ/2 plate 303 and the CD/DVD horizontal/vertical polarizedbeams of specific sizes B_(CD&DVD) are also introduced with apredetermined angle with respect to the horizontal/vertical polarizedreference beams B_(REF). The interference pattern between the referencebeams B_(REF) and the CD/DVD horizontal/vertical polarized beams ofspecific sizes B_(CD&DVD) is recorded on the holographic polarized beamsplitter 304. In the reproduction mode, only the horizontal/verticalpolarized beams B_(REF) are introduced so that the reproduced beamsB_(CD&DVD) ^(RE) corresponding to the CD/DVD horizontal/verticalpolarized beams of specific sizes B_(CD&DVD) are produced along theincident direction of the CD/DVD horizontal/vertical polarized beams ofspecific sizes B_(CD&DVD).

Since the polarization direction is changed by the λ/2 plate 303, noadditional device is required to move or rotate the holographicpolarized beam splitter 304. The beam expander 321 must be added inorder that only two horizontal/vertical polarizations are used forchanging the beam factor of the CD/DVD beams into that of theholographic beam.

In the CD/DVD mode, the λ/2 plate 303 is controlled to make thedirection of the beam be oriented to be horizontal or vertical. Thehorizontal/vertical polarizations correspond to the CD and the DVD mode,respectively, and the reproduced beams B_(CD&DVD) ^(RE) with thecorresponding beam sizes are generated to be illuminated to the beamsplitter 306. The beam splitter 306 divides the reproduced beamB_(CD&DVD) ^(RE) into a reflected beam and a transmitted beam and theshutter 318 makes the reflected beam shut off. The remaining process isthe same as that of the CD/DVD mode of the holographic digital datastorage system shown in FIG. 1.

In the holographic mode, the λ/2 plate 303 is rotated by a predeterminedpolarization angle so that the polarization of the beam may be changed.The polarization angle is not limited and the beam with a predeterminedpolarization angle is introduced into the holographic polarized beamsplitter 304 as a reference beam. The holographic polarized beamsplitter 304 generates the reproduced beam B_(CD&DVD) ^(RE)corresponding to the horizontal and the vertical components of thereference beam B_(RED) and the beam splitter 306 divides the reproducedbeam B_(CD&DVD) ^(RE) into a holographic reference beam and aholographic signal beam. The holographic reference beam proceeds throughthe path B and the holographic signal beam proceeds through the path Aso that an interference pattern is recorded on the medium 310. The beamexpander 321 is added on the path A in order to control the beam size ofthe holographic signal beam. In the reproduction mode, the shutter 318is controlled in order that only the holographic reference beam isintroduced to the medium 310 and a holographic reproduced beamcorresponding to the holographic signal beam is generated. Theholographic reproduced beam is displayed on the CCD 314.

Referring to FIG. 5, there is illustrated a block diagram of aholographic digital data storage system 500 compatible with a CD/DVDplayer in accordance with a third embodiment of the present invention,wherein the holographic storage system 500 comprises a light source 502,two λ/2 plates 503 and 532, a holographic polarized beam splitter 504, abeam splitter 506, four lenses 508, 524, 526 and 528, a medium 510,three mirrors 512, 520 and 530, a charge coupled device (CCD) 514, aphotodiode (PD) 516, a shutter 518 and a spatial light modulator (SLM)522. In the holographic digital data storage system 500 shown in FIG. 5,the optical path of the CD/DVD mode is different from that of theholographic mode. In comparison with the fist embodiment shown in FIG.1, two λ/2 plate 503 and 532, the holographic polarized beam splitter504, the lens 528 and the mirror 530 are added and the shutter 518 ismoved.

The λ/2 plate 503 allows the polarization direction of the linearlypolarized beam introduced from the light source 502 to be rotated by apredetermined angle. The beam with the rotated polarization direction isintroduced to the holographic polarized beam splitter 504.

The holographic polarized beam splitter 504 is made of a higherbirefringence material such as LiNbO₃ or BaTiO₃. Since the refractiveindex difference between the ordinary beam and the extraordinary beammay be used, the reproduced beams may be selectively generated inaccordance with the reference beams with different polarizationdirections.

Referring to FIG. 6, there is illustrated an embodiment of theholographic polarized beam splitter 504 made by using the birefringencecharacteristics. It is assumed that CD/DVD horizontal/vertical polarizedbeams of specific sizes B_(CD&DVD) are used to reproduce the CD playerand the DVD player, respectively and holographic horizontal/verticalpolarized beams of specific sizes B_(HDDSH) and B_(HDDSV) are used toreproduce the holographic signals. The CD/DVD horizontal/verticalpolarized beams of specific sizes B_(CD&DVD) have the beam sizes and thebeam shapes required in the CD player and the DVD player, respectively.The horizontal/vertical polarized reference beams B_(REF) are introducedfrom the λ/2 plate 503 and the CD/DVD horizontal/vertical polarizedbeams of specific sizes B_(CD&DVD) are also introduced with apredetermined angle with respect to the horizontal/vertical polarizedreference beams B_(REF). The holographic horizontal/vertical polarizedbeams of specific sizes B_(HDDSH) and B_(HDDSV) are also introduced witha predetermined angle from each other. In other words, if the horizontalpolarized reference beam B_(REF) with a horizontal polarized componentis introduced, two horizontal polarized beams of specific sizesB_(CD&DVD) and B_(HDDSH) are recorded on the holographic polarized beamsplitter 504 with two different incident angles and, if the verticalpolarized reference beam B_(REF) with a vertical polarized component isintroduced, two vertical polarized beams of specific sizes B_(CD&DVD)and B_(HDDSV) are recorded with two different incident angles. In thereproduction mode, if only the horizontal polarized reference beamB_(REF) is illuminated, two reproduced beams B_(CD&DVD) ^(RE) andB_(HDDSH) ^(RE) are generated along the incident direction of twohorizontal polarized beams of specific sizes B_(CD&DVD) and B_(HDDSH),respectively. For illustration, it is supposed that the CD/DVDhorizontal/vertical polarized beams of specific sizes B_(CD&DVD) areused to the CD/DVD player, respectively, and the holographichorizontal/vertical polarized beams of specific sizes B_(HDDSH) andB_(HDDSV) are used as a holographic reference beam and a holographicsignal beam.

In the CD mode, the λ/2 plate 503 is controlled to make the direction ofthe beam be horizontally oriented. If only the horizontal polarized beamis introduced into the holographic polarized beam splitter 504, thehorizontally polarized CD reproduced beam B_(CD) ^(RE) and thehorizontally polarized holographic reproduced beam B_(HDDSH) ^(RE) areprovided along the path B and the path C, respectively. The CDreproduced beam B_(CD) ^(RE) is transferred into the shutter 518, thebeam splitter 506 and the lens 508 along the path B and introduced tothe medium 510. The reflected beam of the CD reproduced beam B_(CD)^(RE) reflected by the medium 510 functions as a CD signal beam. The CDsignal beam is further reflected by the beam splitter 506, and proceedsalong the path D to be detected by the PD 516 or the CCD 514. Theholographic reproduced beam B_(HDDSH) ^(RE) is transferred into the λ/2plate 532, the mirror 530 and the lens 528 and introduced into themedium 510. Since, however, the medium 510 is of a reflection type inthe CD mode, the holographic reproduced beam B_(HDDSH) ^(RE) isreflected with the same angle as the incident angle so that the CDplayer may be reproduced with no error. If necessary, a shutter may beadded on the path C.

In the DVD mode, the λ/2 plate 503 is controlled to make the directionof the beam be vertically oriented. If only the vertical polarized beamis introduced into the holographic polarized beam splitter 504, thevertically polarized DVD reproduced beam B_(DVD) ^(RE) and thevertically polarized holographic reproduced beam B_(HDDSV) ^(RE) areprovided along the path B and the path A, respectively. The DVDreproduced beam BDVD^(RE) is transferred through the path B to be usedto reproduce the DVD player while the holographic reproduced beamB_(HDDSV) ^(RE) is reflected by the medium 510 so that it does notinfluence the production of the DVD signal.

In the holographic mode, the λ/2 plate 503 is rotated by a predeterminedpolarization angle so that the reference beam has a horizontal and avertical components. The holographic polarized beam splitter 504 is usedto generate three reproduced beams with three different directions.Since, however, the shutter 518 turns to be shut off, there is no beamproceeding on the path B while there are beams proceeding on the path Aand the path C. The beam on the path A is modulated by the SLM 522 asthe holographic signal beam corresponding to the input signals and,then, introduced into the medium 510. The beam on the path C is used asthe holographic reference beam whose polarization direction turns by 90degrees by the λ/2 plate 532 so that two beams on the path A and thepath C have a same polarization direction. The interference patternbetween the holographic reference beam and the holographic signal beamis recorded on the medium 510. In the holographic reproduction mode, theshutter 518 is controlled to be shut off and the λ/2 plate 503 iscontrolled so that only the horizontally polarized reference beam may beintroduced to the holographic polarized beam splitter 504. The beam onthe path C of two horizontally reproduced beams generated by theholographic polarized beam splitter 504 is used as the holographicreference beam whose polarization direction is rotated by the λ/2 plate532 so that the holographic reference beam may be introduced into themedium 510. Accordingly, the holographic reproduced beam proceeds alongthe extension direction of the path A to be displayed on the CCD 514.

If necessary, the angular multiplexing technique may be used so that theincident angles in the CD/DVD mode and the holographic mode may bechanged to record the beams of specific sizes on the holographicpolarized beam splitter 504. In case the holographic polarized beamsplitter 504 is rotated to record the interference patterns between thereference beam and the beams of specific sizes, the λ/2 plate 503 may beunnecessary and the shutter 518 may be moved to the path A. It isnecessary that the shutter 518 on the path A remains shut off except theholographic recording mode.

Referring to FIG. 7, there is illustrated a block diagram of aholographic digital data storage system 700 compatible with a CD/DVDplayer in accordance with a fourth embodiment of the present invention,wherein the holographic storage system 700 comprises a light source 702,two λ/2 plates 703 and 732, a holographic polarized beam splitter 704,two beam splitters 706 and 734, four lenses 708, 724, 726 and 728, amedium 710, three mirrors 712, 720 and 730, a charge coupled device(CCD) 714, a photodiode (PD) 716, a shutter 718 and a spatial lightmodulator (SLM) 722. In the holographic digital data storage system 700shown in FIG. 7, the optical path of the CD/DVD mode is separate fromthat of the holographic mode. In comparison with FIG. 1, two λ/2 plates703 and 732, the holographic polarized beam splitter 704, the lens 728,the mirror 730 and the polarized beam splitter 734 are added and theshutter 718 is shifted from path A to path B.

The λ/2 plate 703 allows the polarization direction of the linearlypolarized beam introduced from the light source 702 to be rotated by apredetermined angle. The beam with the rotated polarization direction isintroduced to the holographic polarized beam splitter 704.

The holographic polarized beam splitter 704 is made of a higherbirefringence material such as LiNbO₃ or BaTiO₃. Referring to FIG. 8,there is illustrated an embodiment of the holographic polarized beamsplitter 704 made by using the birefringence characteristics. It isassumed that CD/DVD horizontal/vertical polarized beams of specificsizes B_(CD&DVD) are used to reproduce the CD/DVD players, respectivelyand a holographic beam of specific size B_(HDDS) is used to reproducethe holographic signals. The CD/DVD holographic/vertical polarized beamsof specific sizes B_(CD&DVD) and the holographic beam of specific sizeB_(HDDS) are introduced with predetermined angles, respectively. TheCD/DVD horizontal/vertical polarized beams of specific sizes B_(CD&DVD)have the beam sizes and the beam shapes required in the CD/DVD players,respectively. It is preferable that the holographic beam of specificsize be introduced with a polarization angle of 45 degree. Forillustration, it is assumed that the CD/DVD horizontal/verticalpolarized beams of specific sizes B_(CD&DVD) are used to the CD/DVDplayers, respectively, and the holographic beam of specific sizeB_(HDDS) with the polarization angle of 45 degree is divided into ahorizontal and a vertical polarized beam, wherein the horizontalpolarized beam is transmitted and the vertical polarized beam isreflected.

In the CD mode, the λ/2 plate 703 is controlled to make the direction ofthe beam be horizontally oriented. If only the horizontal polarized beamis introduced into the holographic polarized beam splitter 704, thehorizontally polarized CD reproduced beam B_(CD) ^(RE) and thehorizontal component of the holographic reproduced beam B_(HDDS) ^(RE)are provided through the path B and the path C, respectively. The CDreproduced beam B_(CD&DVD) ^(RE) is detected by the PD 716 or the CCD714 after passing through the path B and the path D as illustrated inFIG. 5. The horizontal component of the holographic reproduced beamB_(HDDS) ^(RE) is transmitted by the polarized beam splitter 734 and,then, proceeds through the path C to be reflected by the medium 710without influencing the reproduction of the CD player. If the intensityof the holographic reproduced beam B_(HDDS) ^(RE) is so high that the CDplayer may be abnormally reproduced, a shutter may be added between theholographic polarized beam splitter 704 and the polarized beam splitter734.

In the DVD mode, the λ/2 plate 703 is controlled to make the directionof the beam be vertically oriented. The vertically polarized DVDreproduced beam BDVD^(RE) proceeds through the path B and the path D tobe detected as the CD mode while the vertical component of theholographic reproduced beam B_(HDDS) ^(RE) is reflected by the polarizedbeam splitter 734 and proceeds through the path A so that the DVD playermay be normally reproduced.

In the holographic recording mode, the λ/2 plate 703 is rotated by apredetermined polarization angle so that the reference beam has ahorizontal and a vertical component. The beam required in the CD/DVDplayer is shut off by the shutter 718 on the path B and only theholographic beam is divided into a horizontal and a vertical polarizedbeam by the polarized beam splitter 734. The horizontal polarized beamis transmitted through the polarized beam splitter 734, modified to bevertically polarized and introduced through the path C into the medium710 as the holographic reference beam. In the holographic reproductionmode, the λ/2 plate 703 is controlled so that only the horizontallypolarized reference beam may be introduced to the holographic polarizedbeam splitter 704. The shutter 718 turns to be shut off so that no beamproceeds through the path B. The beam transmitted through the polarizedbeam splitter 734 and the λ/2 plate 732 is introduced through the path Cto the medium 710 as the holographic reference beam so that theholographic reproduced beam is displayed through the lens 726 to the CCD714.

Referring to FIG. 9, there is illustrated a block diagram of aholographic digital data storage system 900 compatible with a CD/DVDplayer in accordance with a first embodiment of the present invention,wherein the holographic storage system 900 comprises a light source 902,two beam splitters 905 and 906, three mirrors 907, 912 and 920, aholographic optical element (HOE) lens 909, a medium 910, a chargecoupled device (CCD) 914, a photodiode (PD) 916, a shutter 918, a beamexpander 921, a spatial light modulator (SLM) 922 and two lenses 924 and926. In the holographic digital data storage system 900 shown in FIG. 9,the HOE lens 909 records two CD/DVD numerical apertures and aholographic numerical aperture by using a spatial multiplexing method oran angular multiplexing method. The HOE lens 909 is made of photopolymerand obtains a diffraction efficiency as much as nearly 100%.

Referring to FIG. 10, there is illustrated an embodiment of the HOE lens909 made by using a spatial multiplexing method. The beams with CD/DVDspecific numerical apertures and a holographic specific numericalaperture are introduced sequentially in accordance with the referencebeam represented by two solid lines. Three different lenses 911 arepreferably used to obtain three different numerical apertures. Forillustration, it is supposed that the HOE lens 909 is made in order tohave a CD numerical aperture at a first location, a DVD numericalaperture at a second location and a holographic numerical aperture at athird location.

The beam generated in the light source 902 is divided into a transmittedbeam and a reflected beam by the beam splitter 905. The transmitted beamis reflected by the mirror 907, transmitted through the beam splitter906 and, then, illuminated to the HOE lens 909 as the reference beam. Asthe HOE lens 909 moves to the locations corresponding to the CD/DVDmodes or the holographic mode, three beams with their correspondingspecific numerical apertures are illuminated through the path B to themedium, respectively. The reflected beam proceeds through the path A.Specifically, the reflected beam is transmitted through the shutter 918and the beam expander 921 that expands the beam into the holographicbeam, reflected by the mirror 920 and modulated by the SLM 922 to beilluminated through the lens 924 into the medium 910 as the holographicsignal beam.

In the CD mode, the shutter is controlled to be shut off so that thebeam proceeds only through the path B. The HOE lens 909 is shifted tothe first location so that the beam with a numerical aperture requiredto the CD player is introduced to the medium 910. The beam is reflectedby the medium 910 and transmitted through the HOE lens 909. The HOE lens909 generates a reproduced beam corresponding to the reflected beam bythe medium 910. The reproduced beam is transmitted to the oppositedirection of the original reference beam. The reproduced beam by the HOElens reflected by the beam splitter 906. The reflected beam is detectedby the PD 916 or by the CCD 914. In the DVD mode, it is sufficient thatthe HOE lens 909 is shifted to the second location.

In the holographic recording mode, the shutter 918 is open and the HOElens 909 is shifted to the third location. The beam on the path Bfunctions as the holographic reference beam and the other beam on thepath A functions as the holographic signal beam. In the holographicreproduction mode, the shutter 918 is shut off and the HOE lens 909 isshifted to the third location so that only the holographic referencebeam is introduced to the medium 910. Accordingly, the holographicreproduced beam corresponding to the holographic reference beam isdisplayed on the CCD 914 located at a position along the extensiondirection of the holographic signal beam.

If necessary, a polarizer or a wave plate is used to control theholographic signal beam on behalf of the shutter 918 and a wave platemay be located before or after the HOE lens 909 in order to control theintensity of the light.

While the invention has been shown and described with respect to thepreferred embodiments, it will be understood by those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. An optical device capable of reproducing optical information from aplurality of optical storage mediums, comprising: a light source forproviding a reference beam; and an optical system including a beamgeneration unit which has a beam pattern storage member storing thereinone or more light beam patterns, wherein the beam generation unitselectively reproduces at least one of the stored light beam patterns inresponse to the reference beam to provide one or more reproduced lightbeams at a time, said one or more reproduced light beams serving toreproduce optical information from one of the optical storage mediums,and wherein the one or more reproduced light beams include a holographicbeam, a CD beam and a DVD beam, and wherein the beam generation unitprovides one of the holographic beam, CD beam and DVD beam according toan incidence angle of the reference beam upon the beam pattern storagemember.
 2. The optical device of claim 1, wherein the beam patternstorage member is a holographic storage medium storing thereininterference beam patterns corresponding to the light beam patterns. 3.The optical device of claim 2, wherein the interference beam patternsare stored by angular multiplexing.
 4. The optical device of claim 2,wherein the interference beam patterns are stored according to apolarization angle of the reference beam.
 5. The optical device of claim4, wherein the one or more reproduced light beams include a holographicbeam, a CD beam and a DVD beam.
 6. The optical device of claim 5,wherein, when the reference beam has a first and a second polarizationangle, the CD beam and the DVD beam are provided, respectively, and theholographic beam is obtained by expanding beam size of the CD beamand/or the DVD beam by using a beam expander.
 7. The optical device ofclaim 5, wherein the CD beam and a first component of the holographicbeam are generated when the reference beam has a first polarizationangle; and the DVD beam and a second component of the holographic beamare generated when the reference beam has a second polarization angle,the first and the second components of the holographic beamcorresponding to either of a holographic reference beam and aholographic signal beam, respectively.
 8. The optical device of claim 7,wherein the first and the second components of the holographic beam areprovided with two different projection angles, respectively, withrespect to the beam pattern storage member.
 9. The optical device ofclaim 7, wherein the first and the second components of the holographicbeam are provided with an identical projection angle with respect to thebeam pattern storage member.
 10. The optical device of claim 2, whereinthe one or more reproduced light beams have different numericalapertures and are provided according to a location of the beam patternstorage member with respect to the reference beam.